Answer:
Prime factorisation of the numbers -
[tex] \\ \sf \: 35 = 7 \times \underline5 \\ \\ \sf \: 20 = \underline5 \times 4 \\ \\ \sf \: 15 = 3 \times \underline5 \\ [/tex]
As, we can see that the 5 is common in the both three numbers. So,
GCF, greatest common factor (35, 20, 15) = 5
